Thermal Management for a Ruggedized Electronics Enclosure

ABSTRACT

The present invention relates to a liquid cooling assembly for cooling electronic components. The liquid cooling assembly contains a heat spreader plate for providing mechanical support and thermal dissipation; a fluid channel for directing a cooling fluid in the plane of the heat spreader; and a bottom plate for protecting against destructive shock events and for providing thermal dissipation. The present invention also provides a maze structure in the liquid cooling assembly to increase structural stability against destructive shock events. The present invention also relates to a ruggedized electronics enclosure for housing electronic components. A top compartment contains a first electronics layer and a second electronics layer adjacent to said first electronics layer and a cooling assembly. A thermal shunt is configured to channel heat from the first and second electronics layers to the cooling assembly and to provide additional mechanical support to protect against potentially destructive shock events.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/207,672 that wasfiled on Aug. 19, 2005, which in turn is a continuation-in-part of U.S.Ser. No. 11/203,005 that was filed on Aug. 11, 2005, which in turn is acontinuation of U.S. Ser. No. 10/850,523 that was filed on May 19, 2004and has now issued as U.S. Pat. No. 6,944,022, issued Sep. 13, 2005which in turn is a continuation of U.S. Ser. No. 10/232,915 that wasfiled on Aug. 30, 2002 and has now issued as U.S. Pat. No. 6,765,793,issued Jul. 20, 2004, which applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related to enclosures for electronic circuits andparticularly to the thermal management of ruggedized enclosures for usein installations subjected to hostile environments, includingdestructive shock events and destructive vibration events.

2. Description of the Related Art

Conventional ruggedized electronics enclosures are often employed inmilitary applications. The environments in which military electroniccircuits must be able to operate typically present conditions outside ofa commercial electronic circuit's operational parameters. Examples ofsuch conditions include excessive moisture, salt, heat, vibrations, andmechanical shock. Historically, military electronic equipment was custommade to provide the required survivability in the hostile environments.While effective in surviving the environment, custom equipment is oftensignificantly more expensive than commercial systems, and is typicallydifficult if not impossible to upgrade to the latest technologies.Therefore, a current trend in conventional military hardware is to adaptcommercially available electronics for use in military applications.These systems are typically known as Commercial Off The Shelf systems,or COTS.

The COTS design philosophy has allowed the military to keep current withtechnological innovations in computers and electronics, withoutrequiring specialized and dedicated electronic circuit board assemblies.The COTS design methodology is attractive because of the rapidlyincreasing computational power of commercially available,general-purpose computers. Since the components in a COTS system arecommercially available, though usually modified to some extent, themilitary can maintain an upgrade path similar to that of a commercial PCuser. Thus the COTS philosophy allows the military to integrate the mostpotent electronic components available into their current hardwaresystems.

While COTS systems have allowed the military to reduce the cost ofequipment and to make more frequent upgrades to existing equipment,there are inherent disadvantages to COTS systems. As noted above,military applications must be able to withstand various environmentalextremes, including humidity, temperature, shock and vibration. Theseconditions are typically outside of the operating parameters ofcommercial electronics and, thus, added precautions and modifications tothe physical structures of the equipment must be made to ensurereliability of operation in these environments. Conventional COTSsystems typically use two specialized modifications to maintainreliability. These approaches may be used separately, or in combination.

To deploy COTS equipment in hazardous environments, COTS components arehoused in a complex ruggedized enclosure or case. One approach,sometimes referred to as “cocooning” places a smaller, isolatedequipment rack within a larger, hard mounted enclosure. With thisapproach shock, vibration and other environmental extremes areattenuated by the isolation system to a level that is compatible withCOTS equipment. Another approach, sometimes called Rugged, Off The Shelf(ROTS) seeks to “harden” the COTS equipment, in a manner such as to makeit immune to the rigors of the extended environmental conditions towhich it is exposed. This later approach strengthens the equipment'senclosure and provides added support for internal components. Bothcocooning and ROTS design methodologies must also improve coolingefficiency to accommodate higher operating ambient temperatures. Bothapproaches suffer from added complexity, size, weight and cost.

Commercial systems are typically designed around three main criteria,cost, time-to-market and easy expansion. To deliver on all three designgoals, the assumption is that the environment for the system will not beexposed to extreme environmental conditions. Cost is the primarymotivator to keeping the packaging simple and inexpensive. The packagesupport structures may have a low cost to keep the system cost fromescalating. Keeping costs down to a minimum is counter to therequirements of making a system robust enough to survive a militaryenvironment.

To easily accommodate system expansion, computer manufacturers try tosimplify the installation of peripheral cards, memory and storage. Theidea of having a minimum number of fasteners (i.e., a snap-in-placedesign) allows the customer easy access and installation of peripherals.The design's modularity preserves the customer's investment. When youcouple the commercial constraints with the requirements of the militaryenvironment, the design requires a different approach, typically movingthe structural changes to the system enclosure and it's attachments. Theusual cocooning approach is to design the enclosure to absorb as much ofthe shock as possible to allow the incumbent system to survive theenvironment. In practice, this is not easily achieved, especially whenusing larger and heavier computer systems. Thus, the idea of completelyisolating a commercial system from the rigors of the militaryenvironment is difficult to achieve and adds a large cost premiumbecause the rack is the item being modified. The current solution tosupporting COTS technology in a military environment described above,adds significant complexity to the system.

Two of the most difficult conditions to design for are vibration andmechanical shock. Mechanical shock and vibration may over time destroyelectronic equipment by deforming or fracturing enclosures and internalsupport structures and by causing electrical connectors, circuit cardassemblies and other components to fail. In military applications, aswell as in commercial avionics and the automotive industry, electronicsmust be able to operate while being subjected to constant vibrationalforces generated by the vehicle engines, or waves, as well as beingsubjected to sudden, and often drastic, shocks. Examples of such shocksare those generated by bombs, missiles, depth charges, air pockets,potholes, and other impacts typically encountered by military orcommercial vessels. Furthermore, these conditions may also be seen inthe operating conditions of a network or telephone server during anearthquake. While providing some protection from shock and vibration,the conventional ruggedized enclosure operating alone cannot provideadequate protection for mission-critical electrical components andcircuits.

In order to provide additional protection against shock and vibration,conventional COTS systems mount the ruggedized enclosures describedabove in a mechanically isolated cocoon. FIG. 1 illustrates aconventional mechanically isolated cocoon. As illustrated in FIG. 1, acocoon 100 is provided to house the various ruggedized enclosures 110.The cocoon 100 may be attached to a floor 130 and/or a wall 140 of itssurroundings. Commonly this includes the fuselage or deck plate of amilitary vehicle. The cocoon 100 is attached to the surroundings 130,140 via mechanical isolators 120. A particularly advanced mechanicalisolator 120 is the polymer isolator illustrated in FIG. 1, thoughconventional systems may use any spring-like apparatus to provide theisolation. By attaching the cocoon 100 to its surroundings 130, 140 viamechanical isolators 120, the cocoon 100 is allowed limited movementwith five degrees of freedom. This limited movement helps to dampen theeffects of shock and vibration.

There are several drawbacks to using the mechanically isolated cocoon100. The size and complexity of the cocoon 100 exacerbates the need forefficient heat-removal from the enclosure. Often complex heat flowroutes must be devised in order to maintain a desirable operatingtemperature of electronic components within the cocoon 100. Takentogether, these design considerations drastically increase the cost andcomplexity of such an enclosure.

Some conventional electronics enclosures, like the cocoon 100, rely on aliquid cooling system for stabilizing the internal operatingtemperatures of mounted circuit boards. Conventional liquid cooledenclosures are provided with a heavy cold plate containing boredchannels for a liquid cooling assembly to pass through. The cold platecan be manufactured from a variety of thermally conductive materials toassist in dissipating the heat generated from electronic circuit boards.However, the reliance of conventional liquid cooling systems upon thetraditional cold plate arrangement drives up the cost and overall weightof the assembly.

Various heat-removing methods are known to industries outside of theruggedized electronics markets. In a typical semiconductor device heatmanagement arrangement, a material with a moderately high thermalconductivity, like aluminum, is deposited upon a lower thermallyconductive substrate like silicon. A highly thermally conductive layer,like pyrolytic graphite or copper, is then deposited on top of themoderately high thermally conductive layer. Finally, a layer ofsemiconducting material (or active material) is deposited on top of thehighly thermally conductive material to complete the semiconductingdevice. The three layers of thermally conductive material underneath theheat generating active layer provide adequate heat spreading throughoutthe conductive layers. In some conventional heat sinking techniques, adiamond pin is embedded within the pyrolytic graphite such that heat candissipate away from the active layer in a direction different from thedirection of heat dissipated by the thermally conductive layers.

However, several drawbacks arise when applying conventionalsemiconductor device heat dissipation techniques to large areaelectronics encompassing multiple stacks of electronic layers. Even moredrawbacks are present when applying these heat dissipation techniques tolarge area electronics operating in an environment conducive todestructive shock events and destructive vibration events. Relying upona conventional heat management system is too expensive because of theneed for multiple thermal layers, each with their own unique thermalconductivity to surround the electronic board. Also, introducingmultiple thermal layers would increase the weight and reduce thestructural integrity of a ruggedized electronics enclosure.

What is needed is a ruggedized enclosure for use in hostile environmentswhich is capable of efficiently dissipating heat generated by enclosedelectronic circuitry through the use of a lightweight, cost-effective,structurally sound liquid cooling assembly.

In addition, what is needed is a ruggedized enclosure for use in hostileenvironments which: is 1) lightweight; 2) cost-effective; 3) capable ofproviding a structurally sound housing for packaged electronic layers;and 4) capable of efficiently dissipating heat generated by multiplelayers of electronics.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations and disadvantages ofconventional thermal management techniques used in electronicsenclosures that operate in harsh environments.

According to one embodiment, the present invention provides a layer offoam or foam-like structure surrounding the fluid channels of a liquidcooling assembly for adaptation to a ruggedized enclosure. Grooves arebored through an upper portion of the foam structure to hold the fluidchannels. In an embodiment, support structures surround the foamstructure and can be reinforced with carbon fiber or other high tensilestrength materials to provide the cooling assembly with a mechanicallyrigid “skin.” The foam structure of the present invention provides bothmechanical support and thermal heat dissipation.

According to one embodiment, the present invention includes a maze typestructure surrounding the fluid channels of a liquid cooling assembly.This maze or support structure includes grooves through an upper portionof the maze structure such that fluid channels can be secured to theupper portion of the maze structure. According to one embodiment, themaze structure includes a matrix of cells fabricated from high tensilestrength material. The maze structure of the present invention providesboth mechanical support and thermal heat dissipation.

In one embodiment, a ruggedized electronics enclosure is provided with afirst electronics layer placed adjacent to a cooling assembly. Theruggedized electronics enclosure contains a first and second electronicslayer, a first and second thermal interposer, a thermal shunt, and acooling assembly. The first thermal interposer is placed adjacent to thefirst electronics layer. The second electronics layer is placed adjacentto the first thermal interposer. The second thermal interposer is placedadjacent to the second electronics layer. The first and second thermalinterposers provide heat dissipation away from the first and secondelectronics layers. The thermal shunt provides a thermal connectionbetween the first electronics layer, the second electronics layer, andthe cooling assembly. In an embodiment, the thermal shunt is boredthrough the first electronics layer, the first thermal interposer, andthe second electronics layer.

In one embodiment, the electronics enclosure includes a top compartmentfor housing the electronic circuit, and a cooling assembly attachedthereto. The top compartment may be sealed to further protect theelectronic circuit from moisture and unwanted particles in the air. Thecooling assembly includes a rigid truss plate structure which forms astructural member for rigidifying the enclosure, and also forms anefficient heat radiator for removing heat from the electronic circuit.The truss plate structure achieves it's high strength to weight ratio ina manner similar to conventional “honey-comb” or sandwich structures.The truss plate structure converts bending mode forces, applied toopposing plates, into compression and extension mode forces. However,unlike conventional “honey-comb” or sandwich constructions, the presentinvention provides ducts or passage ways through which cooling air (orother cooling fluid) is allowed to flow to aid in the efficient removalof heat from the top compartment. In an alternate embodiment, the trussplate structure is a honey-comb truss structure that provides passagesthrough which cooling air (or other cooling fluid) is allowed to flow.

In one embodiment, the rigid truss plate structure is formed from apassive radiator coupled between a heat spreader plate and a bottomplate. The heat spreader plate also forms the bottom of the topenclosure and provides both mechanical and thermal coupling between thetop compartment and the cooling assembly. In one embodiment, the passiveradiator may be comprised of a corrugated fin. In another embodiment,the passive radiator is comprised of triangularly shaped fins (anA-frame structure). Both the corrugated fin and the triangular finstructure may provide additional protection against destructive shearand twisting of the enclosure. In another embodiment, the passiveradiator is comprised of a pin-style heatsink. In one embodiment thepin-style heatsink is arranged according to a pin density pattern tocreate a turbulence gradient for the cooling assembly.

In one embodiment, the enclosure is rigidified by the truss platestructure in order to protect the electronic circuit against ananticipated destructive shock event. In one embodiment, the enclosureand circuit can withstand and survive a 60 G shock event. In alternateembodiments the enclosure is designed based upon various criteria suchthat a particular enclosure and enclosed device (e.g., circuit) isdesigned to withstand and survive shock events in the range of 20 G toat least 60 G depending upon these design criteria. In anotherembodiment, the enclosure's resonant frequency is raised above ananticipated destructive vibration event. In one embodiment, of specialinterest for land vehicle or aircraft applications, the enclosure andcircuit have a resonant frequency in the range of 200 Hz to at least 1kHz. In another embodiment, of special interest for shipboardapplications, the enclosure and circuit have a resonant frequency in therange of 20 to 40 Hz. The listed ranges are merely exemplary, andalternate embodiments may have a resonant frequency selected to behigher than a known destructive vibration event.

In one embodiment, the cooling assembly further provides heat pipes fordrawing away additional heat from the electronic circuit and deliveringit to an external heat exchanger. In one embodiment, the heat pipescooperate with the passive radiator to provide an efficient heatexchanger.

In one embodiment, the electronic enclosure includes the use ofmicrochips. These chips may be placed top-down on the heat spreaderplate in order to provide a more efficient heat transfer from the chipto the cooling assembly.

A method for protecting and cooling an electronic circuit via a rigidtruss plate structure is also provided.

The features and advantages described in the specification are not allinclusive, and particularly, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification and claims herein. Moreover, it should be notedthat the language used in the specification has been principallyselected for readability and instructional purposes, and may not havebeen selected to delineate or circumscribe the inventive subject matter,resort to the claims being necessary to determine such inventive subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional mechanically isolated cocoon system.

FIG. 2 illustrates an exploded view of a ruggedized electronicsenclosure according to one embodiment of the present invention.

FIG. 3 illustrates a cut-away structural detail of the assembledruggedized electronics enclosure according to one embodiment of thepresent invention.

FIG. 4 illustrates a cut-away diagram of the ruggedized electronicsenclosure showing heat and airflow related to the enclosure according toone embodiment of the present invention.

FIG. 5 illustrates a cooling assembly utilizing a triangular finstructure.

FIG. 6 illustrates a cooling assembly utilizing a pin-style heatsink.

FIG. 7 illustrates a cooling assembly utilizing a pin-style heatsinkforming a turbulence gradient.

FIG. 8 illustrates a liquid cooling assembly utilizing structural foamin accordance with one embodiment of the present invention.

FIG. 9 illustrates a cross-sectional view of the liquid cooling assemblyof FIG. 8 according to one embodiment of the present invention.

FIGS. 10A-10B illustrate a liquid cooling assembly utilizing a maze ofwalls structure in accordance with an embodiment of the presentinvention.

FIG. 11 illustrates a ruggedized electronics enclosure with anarrangement of thermal shunts in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention is now described withreference to the figures where like reference numbers indicate identicalor functionally similar elements. Also in the figures, the left mostdigit(s) of each reference number correspond(s) to the figure in whichthe reference number is first used.

The present invention relates to a ruggedized electronics enclosure forprotecting electronic circuits that must be able to survive and operateunder harsh conditions such as those in military and automotiveenvironments. The enclosure must be able to protect the electroniccircuits from severe vibration and shock, heat, moisture, dustparticulate, and various other adverse conditions. Throughout thisdescription, the word “destructive” will be used to indicate a force orevent which may cause the enclosure or the electronic circuit to failafter a single occurrence of the event, or after repeated occurrences ofthe event between maintenance intervals. Specific destructive eventswill be discussed in more detail below.

FIG. 2 illustrates an exploded view of a ruggedized electronicsenclosure 200 according to the present invention. As illustrated in FIG.2, the enclosure 200 is configured to house and protect a computeelement 210. The compute element 210 is chosen by way of example asillustrative of the primary features and operation of the enclosure 200,and one skilled in the art will recognize that the enclosure 200 may beconfigured to house and protect any electronic circuit. Examples ofalternate electronic circuits include various other components used in acomputer, ordinance guidance and communication boards, vehicle controlmodules, radio and communications equipment, radar equipment, etc. Aswill be discussed below, the enclosure 200 may most advantageously beused for any electronic circuit which may be formed having a lowvertical profile, but may be used to add increased protection to anydimensioned electronic circuit.

The ruggedized electronics enclosure 200 includes a top compartment 220for housing the electronic circuit 210 (illustrated as a computeelement), and a cooling assembly 230 coupled to the bottom of the topcompartment 220. As illustrated, the enclosure 200 is shaped as arectangle, however any footprint shape may be used. Non-rectangularshapes may be preferred in applications where space is at a premium,such as in aircraft, or military ordinance.

The top compartment 220 includes a top cover 222, one or more thermalinterposers 224, a pair of side walls 226, a front wall 227, a rear wall(not shown) and a heat spreader plate 240. In one embodiment, the sidewalls 226, front wall 227 and rear wall as well as the top cover 222 areformed from aluminum. Alternatively, these portions of the topcompartment 220 may be may be formed of any rigid material including,but not limited to steel, and plastics. Preferably, side walls 226 aresized to extend the entire combined height of the top compartment 220and cooling assembly 230. Front wall 227 and rear wall are preferablysized to extend the height of the top compartment 220. An upper portionof side walls 226, front wall 227, the back wall, top cover 22 and heatspreader plate 240 cooperate to form the sealed top compartment 220 forhousing the electronic circuit 210. In another embodiment, the topcompartment 220 may not be sealed, but may instead be open to theenvironment. The various parts which form the top compartment 220 may becoupled together using screws or other fastener types that may requirespecial tools for removal. Additionally, the screw fasteners may beaugmented by other self-aligning/locking mechanical components. Byutilizing screw fasteners or other removable fasteners, the topcompartment 220 may be opened as necessary to provide service to theelectronics housed inside. Alternatively, the compartment structures, ora substructure therein, may be formed by milling or casting a singlepiece of material such as aluminum, steel or plastic. Anotheralternative includes welding the elements comprising the top compartment220 together to form a solid enclosure. However, while welding mayincrease structural stability, it decreases the enclosure's 200serviceability.

The cooling assembly 230 is coupled to the bottom of top compartment 220and further includes a passive radiator 232 (here illustrated in oneembodiment 232 a) and a bottom plate 234. The passive radiator 232 andbottom plate 234 are coupled to the cooling assembly 230 in order todraw heat away from the highest dissipation components (the topcompartment 220) to a high efficiency heat exchanger (the passiveradiator 232).

As illustrated, the passive radiator 232 may be formed from an aluminumcorrugated fin 232 a. As will be discussed below, the use of an aluminumcorrugated fin 232 a provides specific advantages over other passiveradiators, however, one skilled in the art will recognize that otherpassive radiators may be used in place of the corrugated fin 232 a, aswell as that the radiator 232 may be made from other material aside fromaluminum. For example, the passive radiator may be formed from copper,carbon fiber, composite structures of aluminum and copper or plastic,and may additionally be used in conjunction with heat-pipes and coldplates. Additionally, other structures aside from a corrugated fin 232 amay be used. FIG. 5 illustrates a triangular fin, or A-frame, trussstructure 232 b preferably formed from aluminum or steel. As will bediscussed below, this embodiment of the passive radiator 232 is moredifficult and more expensive to manufacture, but provides additionalstructural integrity to the enclosure 200. FIG. 6 illustrates anotherembodiment of the passive radiator 232 utilizing pin-style heat-sinks232 c positioned between the heat spreader plate 240 and the bottomplate 234. This forms a rigid truss plate structure while allowing somemeasure of heat dissipation profiling based on the placement and densityof the pins.

In general, heat spreader plate 240, a lower portion of side walls 226,and bottom plate 234 cooperate to “sandwich” the passive radiator 232into a solid rigid truss plate structure. The truss plate structureachieves a high strength to weight ratio by converting bending modeforces, applied to opposing plates, into compression and extension modeforces. This is similar to plates formed from conventional honey-comb orsandwich construction. However, unlike conventional “honey-comb” orsandwich construction, the present invention provides ducts orpassageways through which cooling air (or other cooling fluid) isallowed to flow to aid in the efficient removal of heat from the topcompartment 220.

The cooling assembly 230 may be assembled in a number of ways, with onegoal being to keep the assembly process simple, while preservingstructural rigidity and allowing the effective transfer of heat from thebase-plate to the passive radiator 232. One way of doing this with ametallic passive radiator 232 is through welding. If a non-metallicpassive radiator 232 is used, a thermally conductive adhesive may beused.

As illustrated, electronic circuit 210 is a compute element and includesa PCB 212, a plurality of processors 214 coupled to a front of the PCB212, and a plurality of memory components 216 electrically coupled to aback of PCB 212. A thermal interposer 224 a is positioned to contact theback of PCB 212 and the memory components 216 to provide a heat exchangebetween PCB 212 and memory components 216. Typically, the interposer 224is made up of a resilient plastic material, doped with a thermallyconductive and insulating compound such as aluminum oxide, boron nitrideor other materials. Alternatively, the interposer 224 may be formed froma gel or a foam. Alternatively, the top compartment 220 may be filledwith thermally conductive foam. While this alternative providesstructure and heat removal, it is not preferred due to the permanentnature of the installation. A removable interposer 224 is preferred toaid in the keeping the electronics inside the top compartment 220serviceable.

As will be discussed in greater detail below, processors 214 and PCB 212are positioned within top compartment 220 such that processors 214 areplaced in physical contact with heat spreader plate 240, allowing forheat to be conducted away from processors 214. Alternatively, a heatconducting material, such as a thermal interposer similar to interposer224, may be position between the processors 214 and the heat spreaderplate 240. A second thermal interposer 224 is positioned between thememory components 216 and the top cover 222. Top compartment 220 ispreferably sized to provide just enough vertical and horizontal room tofit electronic circuit 210 within its confines. In a preferredembodiment, thermal interposers 224 are created from a resilientmaterial which is slightly compressed to ensure a “snug” fit for theelectronic circuit 210 within top compartment 220. By ensuring that thethermal interposers 224 make tight contact with the top cover 222,additional thermal and structural benefits are realized.

FIG. 3 illustrates a cut-away structural detail of the assembledruggedized electronics enclosure 200. As introduced in FIG. 2, in oneembodiment, the electronic circuit 210 housed in the top compartment 220is again a compute element. One of the objectives for the ruggedizedelectronics enclosure 200 is to provide protection to the electroniccircuit 210 housed in the top compartment 220 from harsh operatingenvironments. As noted above, the top compartment 220 may be completelysealed by appropriately sizing the side walls 226, front wall 227 (notshown), back wall (not shown), top cover 222 and heat spreader plate 240to ensure that no open spaces exist in the top compartment 220 surface.

In addition to being able to make the top compartment 220 airtight,additional steps may be made to “ruggedize” the enclosure 200 to helpreduce the effects of destructive shock events and destructive vibrationevents on the electronic circuit 210 housed within. A destructive shockevent is any shock event that may render the electronic circuit 210 orenclosure 200 inoperative due to a large change in force and momentumbeing applied to the circuit 210 and enclosure 200. The circuit 210 orenclosure 200 may be rendered inoperative after a single destructiveshock event or after a series of destructive shock events occurringbetween maintenance intervals. Examples of destructive shock eventsinclude impacts and explosions from bombs, missiles, other militaryordinance, water craft hitting depth charges, aircraft hitting airpockets, wheeled vehicles hitting potholes as well as other impactstypically encountered by military or commercial vessels. One skilled inthe art will recognize that other destructive shock events exist andthat the above list provides only a general context for the nature of adestructive shock event.

Similarly, a destructive vibration event is any vibration event that maycause the electronic circuit 210 or enclosure 200 to fail due to aweakened structural integrity. Destructive vibration events may beisolated and short-lived in duration or may always be present in theoperating environment. Examples of destructive vibration events includeengine vibrations, turbine vibrations, screw vibrations, prolonged shockevents, travel along uneven surfaces etc. One skilled in the art willrecognize that other destructive vibration events exist and that theabove list provides only a basic context for the nature of a destructivevibration event.

In typical military applications, the electronic circuit 210 must beable to survive and continue to operate efficiently after beingsubjected to an 60 G shock or constant vibration from engines and othermovement. Military specifications MIL810, MIL901, MIL167 and ISO 10055provide specific requirements for shock and vibration resistancedepending on the desired application and are incorporated in theirentireties herein. Typically, the individual chip-level components usedin a standard commercial environment will withstand up to a 60 G shockload. This is due in part to the fact that the interconnects and siliconare packaged such that there is high structural rigidity in thecomponent. However, one concern is with the printed circuit board (PCB)and its assembly. To minimize the shock impact to the PCB and the solderconnections, it is beneficial to have structural ties between the boardand its components and cooling assembly 230.

One design goal is to make the entire enclosure assembly one rigidstructural element in order to protect against destructive shock andvibration events. In one embodiment, the enclosure is rigidified by thetruss plate structure in order to protect the electronic circuit againstan anticipated destructive shock event. In one embodiment, the enclosureand circuit can withstand and survive a 60 G shock event. In alternateembodiments the enclosure is designed based upon various criteria (e.g.,materials, mass, truss plate, dimensions, assembly methods, etc.) suchthat a particular enclosure and enclosed device (e.g., circuit) isdesigned to withstand and survive shock events in the range of 20 G toat least 60 G depending upon these design criteria.

One aspect of forming the enclosure 200 as a rigid structural elementincludes raising the enclosure's 200 resonant frequency to a frequencyhigher than the destructive vibration events to which the enclosure 200will be subject. Two major factors that affect the resonant frequency ofa given structure are the mass, and the material's inherent stiffness.Typically, the lower the mass, the higher the resonant frequency. Thus,the overall mass of the enclosure 200 helps determine the resonantfrequency of the enclosure 200 as well as its susceptibility tovibrational damage. Also, the higher the material stiffness, the higherthe resonant frequency. As noted above, from a vibration standpoint, itis desirable to have the resonant frequency above the frequencies of anyanticipated destructive vibration events to keep the mechanicalstructure from adding to the vibration energy.

Thus, the enclosure 200 is formed from a material that balancesstiffness and mass to provide an overall high resonant frequency whichis higher than the anticipated destructive vibration event frequencies.In the preferred embodiment, the ruggedized enclosure 200 is composedprimarily of aluminum. The use of aluminum offers a good compromisebetween strength needed to protect the electronic circuit 210, whileproviding a lower total mass for the enclosure. As will be discussedbelow, the use of aluminum also provides an efficient way of removingheat generated by the electronic circuit 210. In one embodiment, theenclosure 200 is designed to have a resonant frequency that is at leastapproximately twice the 12-25 Hz frequency of naval shock events. In analternate embodiment, the enclosure 200 has a resonant frequency in therange of hundreds of Hz, to protect the enclosure against an aircraft'sprop or turbine vibrations. The specific resonant frequency chosen willbe dictated by the specific vibrational frequency of the prop or turbineengine used, e.g., between 200 Hz and 1 kHz. These frequencies aremerely examples of the resonant frequencies supported by the presentinvention. Alternate embodiments will have a resonant frequency selectedto be greater than the vibrational frequency of an anticipated shockevent that is to be dissipated by the enclosure 200.

Another aspect of the ruggedized enclosure 200 is its overall profile.In a preferred embodiment, the overall vertical height of the enclosure200 is 1 rack unit (“U”) or 1.75 inches. Additionally, in oneembodiment, the top compartment 220 is configured to house theelectronic circuit 210 snugly, without allowing for significanthorizontal or vertical movement within the compartment 220. Furthercushioning and insulation from vibration is garnered by the use of thethermal interposers 224 which may be compressed slightly to ensure asnug fit while providing an efficient heat conduit to remove heat fromthe electronic circuit 210.

Passive radiator 232 provides additional resistance to destructive shockand vibration events. By using a passive radiator and fluid channelstructure such as the corrugated fin 232 a, the triangular fin 232 b, orthe pin-style heatsink 232 c, a light-weight rigid truss plate structuremay be formed from the cooling assembly 230. This structure is stiffenedby cross coupling (via the passive radiator 232) between the topcompartment 220 and bottom plate 234. By forming the truss platestructure, the passive radiator 232 provides the cooling assembly 230with structural properties similar to a solid thick plate from arigidity standpoint for resisting destructive shock and vibrationevents. While a solid thick plate generally provides additionalstructural integrity to the enclosure 200, there is a tradeoff betweenplate thickness and overall mass. As noted above, the resonant frequencyof the enclosure 200 would be decreased by the increased mass of a solidplate. By instead using a truss plate structure for the cooling assembly230, the enclosure 200 retains the benefit of a thick plate whileavoiding the lower resonant frequency associated with a thick, heavyplate.

In addition to the passive radiator 232, the interposers act to absorbhigh frequency vibrations by acting as lossy dissipative elements. Thecombination of top cover 222, thermal interposers 224, electroniccircuit 210, and cooling assembly 230 in a small vertical space helpsmakes the total enclosure 200 very stiff. Furthermore, the interposersreduce the transfer of energy between the bottom plate 234 and the topcover 222, essentially dissipating the conducted vibrational energy.Additionally, materials used in bottom plate 234, heat spreader plate240 and top cover 222 may be selected to dissipate mechanical(vibrational) energy. In particular, composite materials can offer acombination of high strength (stiffness) and damping (mechanical energydissipation).

As noted above, the truss plate structure helps rigidify the enclosure200 by cross coupling the top compartment 220 and the bottom plate 234.For example, the use of the triangular fin structure 232 b or corrugatedfin 232 a as the passive radiator 232 may also help reduce the effectsof destructive shear events and destructive vibration events in thehorizontal direction indicated by arrow 310 and in a vertical directionindicated by arrow 320. Using a corrugated fin 232 a for the passiveradiator 232 provides a good structure to transfer energy in bothhorizontal and vertical direction. The corrugation directs forces alongthe axes of the structure. The corrugations may also act to reduce thevibrational energy by acting as a dissipative spring. Tying thecorrugations to the top and bottom plate 240, 234 at the peaks stiffensthe structure in the “vertical” direction, effectively raising thestructure's vertical (or bending mode) resonant frequency.

FIG. 4 illustrates a cut-away diagram of the ruggedized electronicsenclosure showing heat and airflow related to the ruggedized electronicsenclosure 200. In FIG. 4, to more clearly illustrate the heatflow andairflow, the top compartment 220 is not fully shown, but it isunderstood that the cooling assembly 230 is coupled to a top compartment220 which houses and protects electronic circuit 210 as illustrated inFIG. 2.

FIG. 4 illustrates two directions for heat flow from electronic circuit210, here illustrated as PCB 212 and processor 214. A primary directionfor heat flow is illustrated by an arrow 410. This heat flow isaccomplished by putting the processor 214 in thermally conductivecontact with heat spreader plate 240. In one embodiment contact may bemade by placing the processor 214 in direct contact with the heatspreader plate 240. Alternatively contact may be made by placing a heatconductive medium between the processor 214 and the heat spreader plate240. Preferably, heat spreader plate 240 has a high thermalconductivity. In a preferred embodiment, processor 214 is oriented to beupside down so that its “top” is pressed against heat spreader plate240. This arrangement allows for direct heat conduction betweenprocessor 214 and heat spreader plate 240. In conventional microchips,the main direction for heat to escape the chip is through its “top”. Bypositioning the top of the processor 214 against the heat spreader plate240, heat is efficiently conducted from the processor 214 to the heatspreader plate 240. Alternatively, the microchips may face with their“tops” away from the heat spreader plate 240 and a thermal interposer224 or other thermally conductive medium may be placed between themicrochip and the heat spreader plate 240.

Heat spreader plate 240 conducts heat away from the electronic circuit210 in the direction indicated by arrow 410, and into the passiveradiator 232. Passive radiator 232 is designed to radiate the heatconducted from the electronic circuit 210 into the environment.Preferably, passive radiator 232 is exposed to an air flow across itssurface area. This air flow is indicated by arrow 430 in FIG. 4. Byinducing an air flow 430 through the spaces formed from passive radiator232 and top and bottom plates 240, 234, heat may be efficiently removedfrom the electronic circuit 210 and from the ruggedized electronicenclosure 200 in general. Alternatively, the cooling assembly 230 can bemounted vertically to allow the heated air to rise, cooling the assemblythrough thermally induced convection currents. The specific proportionsof passive radiator 232 directly affect its efficiency in removing heatfrom the enclosure 200. For instance, the overall height and width of asingle “segment” directly affects the amount of surface area present forradiating heat, as well as changing the profile of the air channels. Theprofile of the air channels affects the channel's impedance to airflowand thus, the rate of airflow (for a given pressure differential)through the air channels of the passive radiator 232 and consequentlythe enclosure 200.

Additionally, for low airflow situations, the cooling assembly 230 isdesigned to radiate the maximum amount of heat to the ambient air.Increasing the surface area increases the heat transfer between theprocessor and the air. This may result in a “tighter” corrugation ormore transitions between the heat spreader plate 240 and the bottomplate 234. If, however, an externally generated pressure differential isused to induce air movement past the passive radiator 232, then thedesign may optimize the passageways through the passive radiator 232 foroptimum heat transfer at a given pressure differential. The size of thepassageways directly affects the impedance of air that may flow acrossthe passive radiator 232. As the passageways decrease in size, the airflow for a given pressure differential, and therefore, the heat transferefficiency of the cooling assembly 230, will also decrease. Thus, onedesign goal is to balance the surface area of the passive radiator 232against the size of the passageways and resultant air flow and heattransfer efficiency. In this way, different operating conditions may bemet by adjusting the proportions of the passive radiator 232 to therequirements of the specific application and environment.

As noted above with respect to FIG. 3, the passive radiator 232 alsoprovides shock and vibration protection. These shock and vibrationaspects of the passive radiator 232 are also dependent on theproportions of each “segment”. It may be necessary to balance theapplication's need for shock and vibration protection against theoperating temperature requirements. Typically, it is required thatsystems operate at ambient temperature extremes above 50 degreesCelsius. Maximum chip case temperatures measured at the package arecommonly specified not to exceed 75 degrees C. For low power devices,this is easily achieved. For higher power devices, the thermalresistance from the electronics to air becomes a significant factor. Inthe case of higher power devices, a different material may be used forthe passive radiator 232 in order to improve the heat transfer to thecooling assembly 230, such as copper or carbon composite materials.

As noted above, heat spreader plate 240 is preferably formed from amaterial with a high thermal conductivity, such as aluminum.Alternatively, the heat spreader plate 240 may be formed from copper ora carbon composite in order to provide a higher thermal conductivity andimproved cooling efficiency at higher rates of airflow. Any type ofmaterial may be used for the passive radiator 232 in this alternateembodiment.

In one embodiment, heat spreader plate 240 or the passive radiator 232may be configured to conduct heat from a “hotter” exhaust side 715 ofthe air channels to a “cooler” inlet side 710, to allow the energy fluxinto the air channel to stay constant, along an axis of the heatspreader plate 240. This can be accomplished by making the heat spreaderplate relatively thicker at the inlet side 710 and thinner at theexhaust side 715. In another embodiment, a turbulence gradient may beachieved by varying the cooling assembly 230 channel capacity, or byvarying the pin density of the passive radiator 232, (if a pin-styleheat sink similar to pin-style heat sink 232 c is used,) by changing theprofile of pins, or by any other means. FIG. 7 illustrates a coolingassembly 230 with a turbulence gradient. The cooling assembly 230 has anintake 710 represented by the air-flow arrow 710 a and an exhaust 715,represented by arrow 715 a. Near the intake 710 of the cooling assembly230 the passive radiator 232 is comprised of elliptical pin fins 232 d.As air moves along the passive radiator 232 from intake 710 to exhaust715, along a direction indicated by arrow 720, the pressure drop alongthe direction 720 of airflow is increased. At the exhaust 715 end of thecooling assembly 230, the pin fins 232 e are shaped to be morecylindrical, which may be similar to the pin style heat sink 232 c.These cylindrical pin-fins 232 e induce more turbulence and thus createa higher pressure drop. The varying turbulence caused by changing thepin profile along arrow 720, tends to keep the rate of energy transferconstant, even though the temperature of the air increases from theintake 710 to the exhaust 715 of the cooling assembly 230. Thisturbulence profiling makes it easier for the heat spreader to maintainan isotherm. The thermal conductivity of the heat spreader can beincreased, usually meaning the mass can be reduced, thus allowing thestructure's resonant frequency (for flexure modes) to be increased, withno reduction in heat transfer efficiency.

The turbulence profiling described above helps maintain several chips incontact with the heat spreader plate 240 at a similar temperature. Thismay be especially helpful in the situation where high rates of airflow430 are induced by an externally generated pressure differential frominlet to exhaust. Referring back to FIG. 4, as the air flows in thedirection of arrow 430, it will be heated by passive radiator 232,thereby reducing its effectiveness in cooling the remainder of thepassive radiator 232. By designing the turbulence profile to match thechanges in airflow temperature, the temperature of the electroniccircuit 210 may be maintained. By maintaining a substantially uniformtemperature across all components in electronic circuit 210, timingvariances due to temperature variations between components may bereduced. This may be especially important if several processors areoperating in parallel.

While the above discussion focused primarily on an embodiment of theenclosure 200 which utilizes an air cooled corrugated fin passiveradiator 232 a, one skilled in the art will recognize that liquids suchas sea water or a commercial refrigerant, other gasses such as gaseousnitrogen, may be used to conduct heat away from the passive radiator232. Alternatively, there may be no liquid or gas present in the systemand thermal transfer is achieved by radiation or convection from theexternal surfaces of the enclosure. One embodiment utilizes a liquidheat exchanger, substituting fluid channels for the passive radiator232. All the mechanical benefits of the truss plate structure would beretained, and the modest increase in mass would be more than compensatedfor in heat transfer efficiency. Another embodiment puts the passiveradiator in physical contact with a cold wall in an aircraft.Additionally, heat pipes may be embedded in the heat spreader plate 240to help remove heat to an external heat exchanger. Additionally, while acorrugated fin 232 a and a triangular fin truss 232 b have proven to beadvantageous from a production and structure standpoint, one skilled inthe art will recognize that other passive radiators are alsocontemplated by this disclosure. Examples of other possible passiveradiators include punched corrugated fins, conventional fin-style heatsinks that may be coupled to the top and bottom plates 240, 234,honey-comb truss structures oriented to allow air to pass through them,or a solid metal plate with longitudinal channels or holes placedtherein.

FIG. 8 illustrates a liquid cooling assembly 800 adapted for coolingelectronic components. The liquid cooling assembly 800 utilizesstructural foam to withstand a destructive shock event in accordancewith an embodiment of the present invention. The cooling assembly 800includes at least the following: a heat spreader plate 240; a pluralityof fluid channels 810; a plurality of fluid channel grooves 840; a layerof structural foam 820; and a bottom plate 234.

In an embodiment of cooling assembly 800, the plurality of fluidchannels 810 are positioned within a plurality of fluid channel grooves840, substantially between the structural foam 820 and the heat spreaderplate 240. The structural foam 820 is positioned in between theplurality of fluid channels 810 and the bottom plate 234. In anembodiment, the plurality of fluid channel grooves 840 are molded intoan outer portion of the layer of structural foam 820 such that theplurality of fluid channels 810 rest within a recess formed by theplurality of fluid channel grooves 840. In one embodiment, the pluralityof fluid channels 810 are thermally adhered to the plurality of fluidchannel grooves 840 with a thermally conductive epoxy. In an alternativeembodiment the fluid channels 852 can be formed as part of the heatspreader plate 240 and can be positioned above the cover plate 854 inone embodiment. The fluid channels 852 can be used in a manner similarto that described with reference to fluid channels 810.

In one embodiment, the plurality of fluid channels 810 provide a conduitfor channeling a cooling fluid through the cooling assembly 800 in orderto draw heat away from the heat spreader plate 240. The plurality offluid channels 810 can be formed from any thermally conductive materiallike copper, aluminum, or a carbon fiber composite. In an embodiment,the plurality of fluid channels 810 can be arranged in a single,serpentine arrangement such that minimal heat buildup occurs within theplurality of fluid channels 810. In an alternate embodiment, the fluidchannels include any number of individual channels that are fed by acommon liquid-producing source. One of ordinary skill in the art willappreciate a variety of geometrical arrangements that the fluid channels810 can take on depending on the particular physical constraintsinherent in a given housing environment. The exact number of fluidchannels is an application-specific parameter that can vary depending onthe precise pressure of fluid flow required to efficiently cool aparticular electronics apparatus.

The cooling fluid (not shown) that passes through the fluid channels 810acts to increase thermal dissipation away from the heat spreader plate240. The cooling fluid can be selected from a group of liquids includingde-ionized water or some mixture of de-ionized water and ethyleneglycol, ammonia, or alcohol. In an embodiment, the cooling fluid passingthrough the plurality of fluid channels 810 is Fluorinert™. One ofordinary skill in the art will appreciate a variety of liquids that areresistant to a variety of environmental conditions, like intense heat,can be used as a cooling fluid.

In one embodiment, the structural foam 820 surrounds the fluid channels810 such that the structural foam 820 provides mechanical rigidityagainst a destructive shock event and thermal conduction of heat awayfrom the heat spreader plate 240. The structural foam 820 can bereplaced with light-weight but stiff, thermally conductive material,thus provides added heat dissipation to cooling assembly 800 bysupplementing the heat dissipation provided by the fluid coolingchannels and heat spreader plate 240. The structural foam 820 alsoprevents deformation against compressive forces. Typically, thestructural foam 820 is formed from a thermally conductive, closed-cellfoam or a porous, open-cell material. Typical porous materials used toform structural foam 820 include styrofoam, styrene-based foam, orurethane-based foam. One of ordinary skill in the art will appreciate avariety of open or closed-cell materials can be used to form structuralfoam 820 such that adequate structural rigidity is achieved to withstanda destructive shock event.

Forming the structural foam 820 with an open or closed-cell foammaterial to support fluid channels 810 of the cooling assembly 800proves beneficial for a variety of reasons. Structural, closed oropen-cell foam is mechanically rigid and thermally conductive. Over alarge area, closed or open-cell foam is relatively non-compressible,thus providing an excellent mechanical buffer for sensitive electroniccomponents during catastrophic shock events. Also, closed or open-cellfoam is lightweight and cost efficient for large-scale use.

A cross-sectional view of cooling assembly 230, as shown in FIG. 9,includes reinforcing fiber 910 embedded within the bottom plate 234 oftruss plate structure. The fiber 910 provides structural reinforcement,stiffening the plate for compression and extension forces in the planeof the plate, that improves the truss section mechanical performance byproviding stiffness for loads that are normal to the plane of the plate.The reinforcing fiber 910 may be oriented in the plane of the surfaceand may contain mixed orientations to improve isotropic stiffness, andmay be formed from carbon or any other high tensile strength materialdepending on the cost and rigidity constraints of a particular coolingapparatus. Structural foam stiffness can also be enhanced with variouslyoriented additives, such as nanotubes or other strength enhancing addmixtures.

FIG. 10A illustrates a liquid cooling assembly 1000, adapted for coolingelectronic components, utilizing a maze of walls structure 1010 adaptedto withstand a destructive shock event in accordance with an embodimentof the present invention. The cooling assembly 1000: a heat spreaderplate 240; a plurality of fluid channels 810; a plurality of fluidchannel grooves 840; a maze structure 1010; and a bottom plate 234. Inan alternate embodiment, the fluid channels 810 may be formed into theheat spreader plate 240, as in the alternate embodiment shown in FIG. 8,in which case the fabrication of maze structure 1010 would be simplifiedbecause the groves 840 would not be required.

According one embodiment, the plurality of fluid channel grooves 840 canbe formed by mechanically boring grooves through an upper portion of themaze structure 1010. Typically, the plurality of fluid channels 810 arethermally adhered to the plurality of fluid channel grooves 840 with athermally conductive epoxy. In an alternative embodiment the fluidchannels 852 can be formed as part of the heat spreader plate 240 asdescribed above. In another embodiment, the fluid channels 810 can beglued or mechanically fastened with fasteners to the upper portion ofthe maze structure 1010. In another embodiment, the fluid channels 810can be coupled to the maze structure 1010 in a similar fashion as thecoupling between the fluid channels 810 and the structural foam 820described, above, in relation to FIG. 8.

The maze structure 1010 of the present invention provides bothmechanical support for cooling assembly 1000 and thermal heatdissipation away from the heat spreader plate 240. In an embodiment, themaze structure can be formed from aluminum, graphite, or a carbon fiber.One skilled in the art will appreciate a variety of metallic orcomposite materials that can form maze structure 1010 to accomplishsimilar structural rigidity and thermal conduction for any particularapplication.

In an embodiment shown in FIG. 10B, the maze structure 1010 includes amatrix of cells 1050 fabricated from a high tensile strength, highlythermally conductive material. For example, the matrix of cells 1050 canbe fabricated from aluminum, graphite, or any particular reinforcedcarbon fiber. In an embodiment, where the dimensions of cooling assembly1000 are approximately 4″×4″, the maze structure 1010 includes at leastnine cells 1050 that form the matrix of cells 1050. The exact number ofcells 1050 contained within the maze structure 1010 depends on the sizeof cooling assembly 1000 and the precise stability requirements neededto withstand a particular catastrophic shock environment. In anembodiment, as shown in FIG. 10B, each cell 1050 within the matrix ofcells can be rectangular in shape. In an alternate embodiment, each cell1050 within the matrix of cells can be square, circular, elliptical,triangular, hexagonal, pentagonal, or other shape. In one embodiment,each cell 1050 within the matrix of cells can be the same regulargeometric shape or each cell 1050 can be a different regular geometricshape. In another embodiment, each cell 1050 can be the same or adifferent irregular geometric shape. One of ordinary skill in the artwill appreciate the cell 1050 formed in any variety of regular orirregular geometric shapes depending on the particular designconstraints of the destructive shock environment. Non-regular shapes maybe preferred in applications where space is at a premium, such as inaircraft, or military ordinance.

FIG. 11 illustrates a ruggedized electronics enclosure 1100 including anarrangement of thermal shunts 1160, in accordance with an embodiment ofthe present invention. In this embodiment, ruggedized enclosure 1100includes a top compartment 220, for housing electronic components and acooling assembly 230. The cooling assembly is mechanically and thermallycoupled to the bottom of the top compartment 220 in order to providestructural support for top compartment 220 along with a means forefficient dissipation of heat generated by electronic components housedwithin top compartment 220. More specific details regarding the couplingof top compartment 220 has been discussed previously with regards toFIG. 2. Some of the components of the ruggedized electronics enclosure1100 have similar function and form as has been described above withreference to FIGS. 2-7, so like reference numerals and terminology havebeen used to indicate similar functionality.

In an embodiment, the top compartment 220 includes: a top cover 222; apair of side walls 226; a front wall 227; a rear wall (not shown); aheat spreader plate 240; a thermally conductive elastomer 1150 adjacentto the top cover 222; a first thermal interposer 224 a adjacent to thethermally conductive elastomer 1150; a first electronics layer 1140adjacent to the first thermal interposer 224 a; a second thermalinterposer 224 b adjacent to the first electronics layer 1140; a secondelectronics layer 1130 adjacent to the second thermal interposer 224 b;one or more electrical connectors 1165 providing electrical couplingbetween the first and second electronics layers 1140, 1130; one or moreair gaps 1145 adjacent to the pair of side walls 226 and the heatspreader plate 240; one or more structural supports 1170 providingmechanical coupling between the second electronics layer 1130 and theheat spreader plate 240; and one or more thermal shunts 1160 positionedadjacent to the first electronics layer 1140, second electronics layer1130, and the heat spreader plate 240.

In one embodiment, the thermally conductive elastomer 1150 is rigidlycoupled in between the top cover 222 of top compartment 220 and one ofthe first thermal interposers 224 a. The thermally conductive elastomer1150 advantageously provides a thermal conduction path from the thermalinterposer 224 to the top cover 222 in order to draw heat away from theelectronic layers. Also, thermally conductive elastomer 1150 providesmechanical dampening from destructive shock vibrations passing betweenthe first thermal interposer 224 a and the top cover 222. In oneembodiment, thermally conductive elastomer 1150 may be formed from anysemi-metallic material that is thermally conductive and mechanicallyresilient. For example, the thermally conductive elastomer 1150 may beformed from aluminum nitride, silicon carbide, or boron nitride. Also,one skilled in the art will recognize that thermally conductiveelastomer 1150 may be formed from a rubberized or plastic material dopedwith a thermally conductive compound like carbon or the like. In apreferred embodiment, thermally conductive elastomer 1150 is createdfrom a resilient material which is slightly compressed to ensure a“snug” fit between first thermal interposer 224 a and top cover 222. Byensuring that the thermally conductive elastomer 1150 makes tightcontact with the top cover 222, additional thermal and structuralbenefits are realized.

In one embodiment, the first thermal interposer 224 a is positionedbetween the first electronics layer 1140 and the thermally conductiveelastomer 1150. By ensuring that the first thermal interposer 224 amakes tight contact with the thermally conductive elastomer 1150,additional thermal and structural benefits are realized. Typically, thefirst thermal interposer 224 a is oriented such that any heat generatedby the first electronics layer 1140 is dissipated away from the firstelectronics layer 1140 in a direction substantially parallel to thefirst electronics layer 1140.

In one embodiment, the first electronics layer 1140 is positioned inbetween the first thermal interposer 224 a and the second thermalinterposer 224 b. The first electronics layer 1140 can be directlyconnected with the second electronics layer by way of electricalconnectors 1165. The resulting combination of the first 1140 and secondelectronics layer 1130, along with the integrated circuits 1175,advantageously provides increased electronic functionality for theparticular system that the ruggedized enclosure 1100 is servicing. Thefirst electronics layer 1140 can include one or more memory components216 as described above.

In an embodiment, the second thermal interposer 224 b is positioned inbetween the first electronics layer 1140 and the second electronicslayer 1130. Typically, the first thermal interposer 224 b is orientedsuch that any heat generated by the first electronics layer 1140 orsecond electronics layer 1130 is dissipated away from the firstelectronics layer 1140 or second electronics layer 1130 in a directionsubstantially parallel to the first electronics layer 1140 or secondelectronics layer 1130. In a preferred embodiment, thermal interposers224 a and 224 b are created from a resilient material which is slightlycompressed to ensure a “snug” fit for the first and second electronicslayers 1140, 1130 within top compartment 220.

The electrical connectors 1165, providing electrical connection betweenthe first and second electronics layers 1140, 1130, may be formed from avariety of electrically conductive materials. In an embodiment,electrical connectors 1165 are formed by embedding a metallic conductor,like copper, within any particular type of plastic material. In anotherembodiment, electrical connectors 1165 are formed by plating a plasticmaterial on its periphery with any particular metallic material.Typically, electrical connectors 1165 are shaped in a regular geometricshape like a cylinder or cube. One of ordinary skill in the art willappreciate a variety of shapes and a variety of materials for formingelectrical connectors 1665 in order to provide sufficient electricalcontact between the first and second electronics layers 1140, 1130.

In an embodiment, the second electronics layer 1130 is mechanicallycoupled to the heat spreader plate 240 by way of structural supports1170. The second electronics layer 1130 preferably includes an etchedcircuit board assembly 212 containing electrically conductive circuitpaths. The second electronics layer 1130 can be constructed from anyinsulating material, like fiberglass or the like, and the conductivestrips are generally laid down onto a surface of the second electronicslayer 1130 through conventional etching techniques.

The structural supports 1170, providing additional support againstdestructive shock events for the second electronics layer 1130, can beformed from a variety of metallic materials like Al, Cu, stainlesssteel, or brass. The structural supports 1170 can function as a“stand-off” such that they physically separate, or hold off, the secondelectronics layer 1130 from the heat spreader plate 240. In anembodiment, the structural supports 1170 provide some thermal heatdissipation away from the second electronics layer 1130. Typically, thestructural supports can be circular or hexagonal in shape depending onpackaging constraints. One skilled in the art will appreciate a varietyof support materials in a variety of shapes that can be used to form thestructural supports 1170 to accomplish similar functionality.

In an embodiment, one or more integrated circuits 1175 are electricallycoupled to a back surface of the second electronics layer 1130 andplaced in direct contact with heat spreader plate 240. Providing directcontact between the integrated circuits 1175 and the heat spreader plate240 allows for heat to be conducted away from the integrated circuits11175.

In one embodiment, one or more thermal shunts 1160 are positionedadjacent to and/or through the first electronics layer 1140, secondelectronics layer 1130, and the heat spreader plate 240 to provide athermal conduction path from the first electronics layer 1140, throughthe second thermal interposer 224 b and the second electronics layer1130, to the heat spreader plate 240. The presence of the thermal shunts1160 provides a direct conduit for thermal energy generated by the firstelectronics layer 1140 to be dissipated by the heat spreader plate 240.The thermal shunts 1160 also provide an avenue for dissipation ofmechanical shock between the heat spreader plate 240 and the layers ofelectronics 1140, 1130. In an embodiment, thermal or mechanical energypassing through the thermal shunts 1160 is in a direction substantiallyperpendicular to the first and second thermal interposers 224 a, 224 b.

In one embodiment the thermal shunts 1160 are coupled by mechanicallyboring a plurality of aligned via holes within the structure of firstelectronics layer 1140, second thermal interposer 224 b, and secondelectronics layer 1130 and positioning each thermal shunt 1160 to fitwithin the plurality of the via holes. The thermal shunts 1160 can becircular or hexagonal or any particular shape depending on theconstraints of the given geometry of the electronics layers throughwhich the thermal shunts 1160 are bored. In another embodiment, thethermal shunts 1160 can be coupled with bent sheet metal and mounted toa bracket on the first and second electronics layers 1140, 1130 with ascrew or fastener. Also, thermal shunts 1160 can be coupled toelectronics layers 1140, 1130 and heat spreader plate 240 by way ofthermally conductive grease.

In one embodiment, two thermal shunts per 4″×4″ electronics layer canproduced adequate heat transfer. One of skill in the art, however, willappreciate any number of thermal shunts per layer of electronics can beused to suit the needs of a variety of applications. The thermal shunts1160 may be arranged in a serial arrangement, where a first thermalshunt 1160 a (not shown) provides thermal connection between the firstelectronics layer 1140 and the second electronics layer 1130 and asecond thermal shunt 1160 b (not shown), serially offset from the firstthermal shunt 1160 a, provides thermal connection between the secondelectronics layer 1130 and the heat spreader plate 240. One skilled inthe art can envision an electronics arrangement including a plurality ofdifferent electronics layers stacked in any particular arrangement wherethe advent of any number of variously arranged thermal shunts 1160 canoffer a direct thermal contact between the each layer within theplurality of different electronics layers and the heat spreader plate240.

In an embodiment, the thermal shunts 1160 are fabricated from a materialwith high thermal conductivity and high structural integrity likegraphite or copper. The thermal shunts 1160 can also be formed from avariety of doped aluminum materials, including AlSiC. In anotherembodiment, the thermal shunts 1160 are formed from sputtered diamond.In another embodiment, the thermal shunts 1160 can be any particularheat pipe arrangement that provides both mechanical structure andconduction of thermal energy. More details regarding a possible heatpipe arrangement for thermal shunts 1160 are found, above, withreference to the descriptions for FIG. 2. One skilled in the art willappreciate a variety of thermally conductive, structurally soundmaterials that can form thermal shunts 1160.

While the invention has been particularly shown and described withreference to a preferred embodiment and various alternate embodiments,it will be understood by persons skilled in the relevant art thatvarious changes in form and details can be made therein withoutdeparting from the spirit and scope of the invention.

1. A liquid cooling assembly for cooling electronic components, thecooling assembly comprising: a heat spreader unit; a structural foamlayer, rigidly coupled to said heat spreader unit, providing mechanicalsupport and thermal dissipation for the electronic components; a fluidchannel, rigidly coupled to said structural foam layer, for directing acooling fluid in a first direction; and a bottom plate rigidly coupledto said structural foam layer, wherein said heat spreader unit, saidstructural foam layer, and said bottom plate providing a rigid structurethat does not substantially deform in response to one or moredestructive shock events, to protect the electronic components againstsaid one or more destructive shock events and to provide thermaldissipation of heat generated by the electronic components.
 2. Theliquid cooling assembly of claim 1, wherein said structural foam layerfurther comprises a fluid channel groove.
 3. The liquid cooling assemblyof claim 1, wherein said fluid channel is adhered to said fluid channelgroove by way of a thermally conductive epoxy.
 4. The liquid coolingassembly of claim 1, wherein said structural foam layer is formed with aclosed-cell foam.
 5. The liquid cooling assembly of claim 1, whereinsaid structural foam layer is formed with a substantiallynon-compressible material that has a substantially high thermalconductivity
 6. The liquid cooling assembly of claim 1, wherein saidbottom plate is embedded with a reinforcing fiber to provide structuralstrength and stiffness for compressive and extension forces, to improvethe normal mode mechanical performance of the truss structure.
 7. Aliquid cooling assembly for cooling electronic components, the coolingassembly comprising: a heat spreader unit; a maze structure, rigidlycoupled to said heat spreader unit, providing mechanical support andthermal dissipation for the electronic components; a fluid channel,rigidly coupled to said maze structure, for directing a cooling fluid ina first direction; and a bottom plate rigidly coupled to said mazestructure, wherein said heat spreader unit, said maze structure, andsaid bottom plate providing a rigid structure that does notsubstantially deform in response to one or more destructive shock event,to protect the electronic components against said one or moredestructive shock events and to provide thermal dissipation of heatgenerated by the electronic components.
 8. The liquid cooling assemblyof claim 7, wherein said maze structure further comprises a matrix ofcells.
 9. The liquid cooling assembly of claim 8, wherein said matrix ofcells are fabricated from a high tensile strength, highly thermallyconductive material.
 10. The liquid cooling assembly of claim 8, whereinsaid matrix of cells is fabricated from aluminum, graphite, or anyparticular reinforced carbon fiber.